Autonomous vehicles and vehicles that include advanced driver assistance systems include steering systems which are responsible for steering, i.e. laterally positioning, the vehicle without physical input from an operator of the automobile during at least some modes of operation of the vehicle. The steering systems of such vehicles include and actuator, for example an electric motor, which positions a steering mechanism, for example, a rack and pinion steering gear which positions steer tires of the vehicle to alter the lateral position or direction of the vehicle. However, it may be desirable for such vehicles to maintain a customary steering input, i.e. a steering wheel, for the operator to steer the vehicle in a conventional manner in some circumstances. When the steering actuator is solely responsible for steering the vehicle, it is common for the steering wheel to be back-driven, i.e. the steering wheel rotates without input from the operator of the motor vehicle due to a mechanical link between the steering mechanism and the steering wheel. While the steering wheel being back-driven may note pose a problem in modes of operation where the rate of rotation and the magnitude of angular movement of the steering wheel caused by the steering actuator is relatively low, for example when the vehicle is navigating a route on a roadway, a risk may be present in a mode of operation where the rate of rotation and the magnitude of angular movement of the steering wheel caused by the steering actuator is relatively high, for example during a parking maneuver or during an evasive maneuver. U.S. Pat. No. 8,002,075 to Markfort discloses a steering system that may be used in an autonomous vehicle. The steering system of Markfort includes a clutch between the steering wheel and the steering mechanism which allows the steering wheel to be decoupled from the steering mechanism during autonomous operation and to be coupled from the steering mechanism outside of autonomous operation. While the steering system of Markfort may eliminate the risk of the operator of the vehicle coming into contact with the steering wheel which is being rotated at a high rate or being rotated through a large angular displacement during autonomous operation, the steering system of Markfort assumes only two operational states are needed, i.e. autonomous and manual. However, it may be desirable for the steering system to have greater flexibility based on the particular driving situation that is encountered.
What is needed is a steering system for an autonomous vehicle which minimizes or eliminates one or more the shortcomings as set forth above.